Computer aided design (CAD) is widely used in the design and manufacture of complex tools. Although a CAD system can simplify the design process, the patterns established by the CAD system must still be projected onto the tool surface for the manufacture of the tool.
In the past, MYLAR sheets with a pattern imprinted thereon have been used to apply the pattern to the tool. This method is satisfactory for planar surfaces or surfaces having a curve in only one dimension. With more complicated surfaces, the MYLAR sheet will not sit flat and therefore the accuracy of the applied pattern is greatly diminished.
Laser scanners such as those described in U.S. Pat. No. 5,237,444 have been used to project a pattern onto a cylindrical object surface. A focused laser beam is deflected by the use of two orthagonally placed scanners causing the laser beam to follow a varying optical path to various object points. The scanners each pivotally rotate a mirror which will direct the laser beam to any point on the object's surface. This type of scanner can accept CAD data. By controlling the axis of rotation of the two mirrors, the scanners can project a vary accurate image onto the object's surface. However, the scanners must be very precisely located relative to the object in order to precisely locate the projected image. Considerable time is therefore necessary in order to precisely calibrate the positioning of the laser head relative to the object.
In still other types of scanners as disclosed in U.S. Pat. Nos. 4,797,747, 4,816,920, 5,048,904 and 5,150,249, scanning systems project an image onto a two dimensional surface. These scanners are used for projecting images for laser printers or reading an image from a surface for facsimile image transmission devices. In this type of apparatus, a beam splitter is used to direct a portion of the laser beam to a photo detector or sensor that monitors the beam intensity and provides a corresponding feedback signal to a logic controller or host computer to maintain a constant beam intensity. By using a beam splitter, the laser beam is attenuated resulting in a loss of power which can be as high as 50%.
Still other optical scanners utilize a conventional laser projector with optical sensors mounted on the object itself. When the laser beam contacts the optical sensor, a corresponding signal is generated and sent back to a logic controller. However, this system requires that the optical sensors be wired directly to the logic controller. In many heavy industrial situations, a series of wires is unacceptable for implementation.
The principal disadvantage of the prior art devices is that each of the devices do not include any effective feedback means for generating a feedback signal without attenuating the laser beam.
Further, accurate projection with a precision of thousandths of an inch from a distance of many feet based on absolute positioning of the laser projector and tool requires elaborate and expensive fixtures, cumbersome operating procedures and would be affected by many possible sources of error.